/*colddays.c -- 多重选择*/
#include "stdio.h"
#include "ctype.h"

int main(void){

    char ch;

    printf("请输入一个字符:");
    ch = getchar();
    if(isupper(ch)){
        putchar(tolower(ch));
    }else if(islower(ch)){
        putchar(toupper(ch));
    }else{
        putchar(ch);
    }
    // putchar(ch);
    // printf("%d",isalnum(ch));
    // printf("%d",isalpha(ch));
    // printf("%d",iscntrl(ch));//判断是否是控制字符;字母其实为0(不是);数字为0;Ctrl+B为1
    // printf("%d",isdigit(ch));//判断是否是数字.是为1；不是为0

    return 0;
}